Emitter: New macro: ENSURE_SIG_STACK, because callers can't check size right.
Emitter: New macro: ENSURE_SIG_STACK, because callers can't check size right.

I tried something a bit more complicated for the emitter and got a few invalid
reads from valgrind. It turns out that a lot of callers were using > instead of
>= against sig_stack_size.

Provide a macro, and likely fix up numerous problems in the process.

boardwalk/lily,crasm/lily,crasm/lily,crasm/lily,boardwalk/lily